The organic solvent development to form a negative pattern is a traditional technique. A resist composition comprising cyclized rubber is developed using an alkene such as xylene as the developer. An early chemically amplified resist composition comprising poly(tert-butoxycarbonyloxystyrene) is developed with anisole as the developer to form a negative pattern.
Recently a highlight is put on the organic solvent development again. It would be desirable if a very fine hole pattern, which is not achievable with the positive tone, is resolvable through negative tone exposure. To this end, a positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. A study is also made to double the resolution by combining two developments, alkaline development and organic solvent development.
As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such pattern forming processes are described in Patent Documents 1 to 3. These patent documents disclose resist compositions for organic solvent development comprising a copolymer of hydroxyadamantane methacrylate, a copolymer of norbornane lactone methacrylate, and a copolymer of methacrylate having acidic groups including carboxyl, sulfo, phenol and thiol groups substituted with two or more acid labile groups, and pattern forming processes using the same.
The positive development system involving deprotection reaction to generate a carboxyl group and subsequent neutralization reaction with aqueous alkaline developer to improve a dissolution rate achieves a high dissolution contrast in that the dissolution rate differs between the unexposed and exposed regions by a factor of more than 1,000. In contrast, the negative development system via organic solvent development provides a low contrast because the dissolution rate in the unexposed region due to solvation is low, and the dissolution rate thus differs between the unexposed and exposed regions by a factor of less than 100. For the negative development system via organic solvent development, it is desired to seek for a novel material which can offer a high dissolution contrast.
When hole patterns are formed by negative development, it is necessary that holes be of uniform size. Since acid diffusion within the resist film proceeds unevenly, it is necessary to further suppress the acid diffusion one step. Fluorinated tetraarylborate is expected to provide low acid diffusion due to its giant molecular weight. Patent Document 4 discloses a positive resist composition of alkaline development type having fluorinated tetraarylborate added thereto.